TEHRAN, Iran -- Iran began loading fuel into the core of its first nuclear power plant on Tuesday, moving closer to the start-up of a facility that the U.S. once hoped to stop over fears of Tehran's nuclear ambitions.

Iranian and Russian engineers started moving nuclear fuel into the main reactor building in August but a reported leak in a storage pool delayed injection of the fuel into the reactor.

"Fuel injection into the core of the reactor has begun," the state television announced.

The U.S. withdrew its opposition to the plant after Russia satisfied concerns over how it would be fueled and the fate of the spent fuel rods.

Worries remain, however, over Iran's program to enrich uranium for nuclear fuel since the process can also be used to create weapons grade material.

Iran says the 1,000-megawatt nuclear plant, built with the help of Russia, will begin generating electricity in early 2011 after years of delays.

Under a contract signed between Iran and Russia in 1995, the Bushehr nuclear power plant was originally scheduled to come on stream in July 1999 but the start-up has been delayed repeatedly by construction and supply glitches.

Iranian officials have sporadically criticized Russia for the delays, some calling Moscow an "unreliable partner" and others accusing Russia of using the reactor as a lever in nuclear diplomacy with Iran.

Russia began shipping fuel for the plant in 2007.

At the plant's inauguration on Aug. 21, Iran's Vice President Ali Akbar Salehi had said loading the fuel into the reactor core would take place over two weeks and the plant would then produce electricity two months later in November.

Earlier this month, he said that the start up was postponed because of a small leak. Originally there had been speculation that a computer worm found on the laptops of several plant employees might have been behind the delay.